Siegele D A, Hu J C
Department of Biology, Institute for Biosciences and Technology, Texas A & M University, College Station, TX 77843, USA.
Proc Natl Acad Sci U S A. 1997 Jul 22;94(15):8168-72. doi: 10.1073/pnas.94.15.8168.
Gene expression from plasmids containing the araBAD promoter can be regulated by the concentration of arabinose in the growth medium. Guzman et al. [Guzman, L.-M., Belin, D., Carson, M. J. & Beckwith, J. (1995) J. Bacteriol. 177, 4121-4130] showed that expression of a cloned gene could be modulated over several orders of magnitude in cultures grown in the presence of subsaturating concentrations of arabinose. We constructed plasmids expressing a fast-folding mutant Aequorea victoria green fluorescent protein from the araBAD promoter to examine the distribution of expressed gene products in individual cells at intermediate induction levels. Microscopic examination of cells grown at low arabinose concentrations shows mixtures of brightly fluorescent and dark cells, suggesting that intermediate expression levels in cultures reflect a population average of induced and uninduced cells. The kinetics of green fluorescent protein induction suggest that this reflects an "autocatalytic" induction mechanism due to accumulation of the inducer by active transport. This mechanism, which is analogous to the induction of the lac operon at subsaturating inducer concentrations in lacY+ cells, was described 40 years ago by Novick and Weiner [Novick, A. & Weiner, M. (1957) Proc. Natl. Acad. Sci. USA 43, 553-566].
含有araBAD启动子的质粒的基因表达可受生长培养基中阿拉伯糖浓度的调控。古兹曼等人[古兹曼，L.-M.，贝林，D.，卡森，M. J. & 贝克威思，J.（1995年）《细菌学杂志》177卷，4121 - 4130页]表明，在含有亚饱和浓度阿拉伯糖的培养物中，克隆基因的表达可在几个数量级范围内进行调节。我们构建了从araBAD启动子表达快速折叠突变型维多利亚多管水母绿色荧光蛋白的质粒，以检测中间诱导水平下单个细胞中表达的基因产物的分布。对在低阿拉伯糖浓度下生长的细胞进行显微镜检查，发现有明亮荧光细胞和暗细胞的混合物，这表明培养物中的中间表达水平反映了诱导细胞和未诱导细胞的群体平均值。绿色荧光蛋白诱导的动力学表明，这反映了一种“自催化”诱导机制，这是由于诱导剂通过主动运输积累所致。这种机制类似于在lacY⁺细胞中亚饱和诱导剂浓度下lac操纵子的诱导，40年前由诺维克和韦纳[诺维克，A. & 韦纳，M.（1957年）《美国国家科学院院刊》43卷，553 - 566页]所描述。
